Reliability of gate oxides in integrated circuits (IC) is of the utmost importance in providing high performance IC chips. The main performance criteria in image sensor IC are, among others, speed, and packing density. As is well known in the field, scaling down, that is reducing device size, has been the chief vehicle for achieving increased packing density. Scaling down device size in turn, means using smaller channel lengths and widths. To increase the speed, the saturation drain current drain current (Idsat) must be increased. It is known that a decrease in either the channel length or the gate oxide thickness (tox) will lead to an increase in Idsat.
While the benefits of using thin oxides are well known in the field, such oxides must exhibit adequate reliability characteristics under normal circuit operating conditions. As additional contributor to the reliability concerns is the damage caused to thin gate oxides when a metal conductor such as the polysilicon gate over gate oxide is locally charged. Such local charging can occur when a semiconductor wafer is subjected to any number of semiconductor processes involving, for example, plasma etching or ion implantation.